The performance of gas turbine engines, whether measured in terms of efficiency or specific output, is improved by increasing the turbine gas temperature. It is therefore desirable to operate the turbines at the highest possible temperatures. For any engine cycle compression ratio or bypass ratio, increasing the turbine entry gas temperature produces more specific thrust (e.g. engine thrust per unit of air mass flow). However, as turbine entry temperatures increase, it is necessary to develop components and materials better able to withstand the increased temperatures.
This has led to the replacement of metallic shroud segments with ceramic matrix composite shroud segments having higher temperature capabilities. To accommodate the change in material, however, adaptations to the segments have been proposed. For example, EP 0751104 discloses a ceramic segment having an abradable seal which is suitable for use with nickel base turbine blades, and EP 1965030 discloses a hollow section ceramic seal segment.
A conventional method of attaching shroud segments to other components is a “birdmouth” type assembly, in which a slot in one component is attached to a hook in another component. When assembled, the two components can then locate across an interface which is perpendicular to the direction of the primary load.
However, such an assembly approach is problematic to implement in a ceramic matrix composite component. For example, when the slot is cut into such a component, reinforcing fibres in the composite may be severed, Further, undesirable stress concentrations may be formed at the base of the slot.